Electric regulator



Nov. 2, 1948. J. L. STRATTON ELECTRIC REGULATOR Filed March 21, 1946 Ir? Jerry L. stratbon,

enter:

gm m

by His Attorney.

Patented Nov. 2,

ELECTRIC REGULATOR Jerry L. Stratton, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application March 21, 1946, Serial No. 655,981

11 Claims. 1

My invention relates to an electric regulator and more particularly to an electric regulator of the electronic type for controlling an electrical condition, such as the voltage orcurrent of an electric circuit or of a dynamo-electric machine,

It is an object of my invention to provide a new and improved electric regulator.

It is another object of my invention to provide a new and improved electronic regulator and regulating system for controlling the voltage or the current of an electric circuit or of a dynamoelectric machine.

It is still another object of my invention to provide a new and improved electronic regulating system for controlling the voltage of a generator and for maintaining its load current constant.

Although my invention may be utilized in various types of circuits for controlling either the voltage or the current of such circuits, I have found it to be particularly well adapted for controlling the voltage and current of a direct current generator provided with a separately excited field winding and an exciter therefore having a separately excited field winding controlled by a controlled electronic network. In accordance with the illustrated embodiment of my invention, I provide an electronic regulator which controls the generator voltage but the voltage so held is modified by a current standard in such a way as to produce a constant load current regardless of variations in the load resistance of the generator.

My invention will be better understood from the following. description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

The single figure of the accompanying drawing is a diagrammatic illustration of one embodiment of my invention arranged for controlling a direct current generator. 7

Referring to the drawing, I have shown an embodiment of my invention for controlling the voltage or current of a direct currentgenerator l provided with an armature output circuit 2 and a .field winding 3. The field winding 3 is illustrated as being energized byan exciter 4 which, in turn, is provided with a separately excited field winding 5. although the excitation of the generator I, if desired, may be obtained directly rather than through the controlled exciter. As illustrated, the field winding 5 of exciter 4 is arranged to be energized from a controlled rectifier 8 which comprises a transformer I having a primary winding 8 and a secondary winding 8 connected through a pair of electronic tubes I and II which are arranged for bi-phase half-wave rectification. The

.2 primary winding 8 of the rectifier transformer 1 is connected to be energized from an alternating current supply bus I2 which, in turn, is connected to be energized from a main alternating current supply circuit 13, preferably through a constant voltage transformer ll, to insure a substantially constant voltage for energizing the various component circuits of the regulator. The electronic tubes l0 and H are preferably of the gaseous type, such as of the thyratron type as illustrated, and each tube is provided with a control electrode to control the desired current for excitation of the exciter field winding 5. Tube H3 is provided with an anode 15, a cathode IS, a control grid l1 and a suppressor grid 18, while tube I i is similarly provided with an anode i9, 9. cathode 20, a control grid 2| and a suppressor grid 22. The suppressor grids l8 and 22 are connected to their respective cathodes in a conventional manner. One terminal of field winding is connected to a midpoint 9' of the secondary winding 8 and the other terminal of field winding 5 is connected to a junction point 23 of the cathodes l8 and also in a conventional manner for bi-phase rectification. The heater circuits for cathodes l8 and 20 have been omitted to avoid complicating the drawing but such heater circuits would be provided for these tubes as well as for the other tubes with heater circuits later described in any conventional manner well known in the art. The control grids H and 2| are connected tobe controlled through a suitable phase shifting means or network 24 which, as illustrated, comprises a transformer 25 having a primar winding 26 connected to be energized from the alternating current supply bus l2, and a secondary winding 27 provided with an electrical mid-point terminal 21' A resistor 28 and a saturable reactor 29 provided with a direct current saturating winding 30 are connected in series relation across the end terminals of the secondary winding 21. A junction terminal 3| is is provided between the resistor 28 and the saturable reactor 29. A grid transformer 32 is provided to obtain a voltage from the phase shift circuit 24 which is variable in phase with respect to the voltage impressed upon the anode-cathode circuits of tubes Ill and H. The grid transformer 32 comprises a primary winding 33 connected between the electrical, midpoint 21' and the junction terminal 3|, and a secondary winding 34 having a midpoint 34 connected to the cathode junction terminal 23 with the end terminals thereof connected through grid resistors SI and 36 to grids I1 and 2|, respectively.

The regulator which controls the energizaamplifying tube 52 by direct coupling.

tion of generator I by controlling the rectifier 8 comprises a voltage standard section 31 and an amplifier section 38. These two sections along with the rectifier 6 and its phase shift circuit 24 may be conveniently mounted on the same panel for unit enclosure as indicated by the dotted rectangle 39. This unit assembly, for ease of identification, will be referred was a "current regulator and is provided with output terminals 60, 4| and 42. Power supply for the voltage standard 31 may be obtained, as illustrated, from an additional secondary winding 63 on the transformer 25. Secondary winding (i3 is provided with a center-tap G3 which is connected to a negative bus conductor 66 of the regulator, while the end terminalsof transformer 23 are connected through a double-anode rectifier tube 65 to a positive bus conductor 15 so as to provide a rectifled direct voltage between conductors 53 3 and 66. Negative bus conductor 38 is connected to output terminal 42 and positive bus conductor 66 is connected to output terminal ill. Constant voltage between'the output terminals 60 and G2 is obtained by means of an electronic tube 6? having an anode 138, a cathode 39, a control grid 50 and a suppressor grid The tube 37 is preferably of the high vacuum type and is connected in series relation with bus conductor :16 to serve as a series variable impedance to maintain the voltage across terminals 36 and 62 at a constant value. The output of the rectifier G5 is preferably filtered by suitable filter means which may comprise a series inductance 135' connected in bus conductor 66 and a pair of capacitors t5" connected on each side of the inductance 65' in parallel relation :2.

across the rectifier output terminals. Theseries impedance regulating tube 67 is controlled by an Tube 52 is preferably a pentode tube of the high vacuum type and is provided with an anode 53, a cathode 56, a control grid 55, a screen grid 56 and a suppressor grid 5?. Tube 52 is connected in series relation with a resistor 58 connected between the tube anode 53 at a junction terminal 59 and the positive conductor 66, and a voltage regulating tube 60 of the glow discharge type connected between the cathode 56 at a junction terminal 6| and the negative conductor M3. The junction terminal 59 is connected to the grid of the series regulating tube so that the resistor 58 is connected in the control grid-cathode circuit of tube 41. The voltage regulating tube 6|] ma ntains the cathode of amplifier tube 52 at a potential fixed relative to the negative bus 44. The tube is connected to the positive bus conductor 46 through a pair of series connected resistors 62 and 63. A junction terminal 66 is provided between the resistors 62 and 63 and is connected to the screen grid 56 of, tube 52 so that the screen grid is maintained at a position potential relative to its cathode 54. The suppressor grid 56 is connected to its cathode in a conventional manner. A capacitor 65 is connected in parallel with glow tube 60 to act as a bypass and filter. A voltage divider comprising series connected resistors 66 and 61 having a junction terminal 68 therebetween is connected across the regulated bus conductors 44 and 46. The junction terminal 68 is connected'to control grid 55 of amplifier tube 52 and thereby impresses upon the control grid 55 any voltage deviation from the standard established by glow tube 60. A

capacitor 69 is connected in parallel with the voltage divider across conductors 44 and 46 to suppress residual voltage ripple of the output circuit 26 and, as illustrated, by varying the sat-- uration of reactor 29 by means of its direct current winding 30. The energization of winding 60 is obtained by connecting this winding across the voltage standard conductors M and 66 through a controlled electronic tube 70. Although any suitable type of tube may be used, I have illustrated tube 70 as being of the high vacuum type with an anode ill, a cathode l2, a control grid 13, a screen grid 76, and a suppressor grid 75. A voltage divider comprising series connected resistors i6 and Ti and having a junction terminal l6 therebetween is connected across the voltage standard bus conductors 66 and 66. The cathode i2 of tube 76 is connected to the junction terminal 73 to maintain the cathode of tube 76 at some predetermined voltage negative with respect to the positive bus conductor 16. The

screen grid ii-'5 of tube is connected to the. junction terminal 66 between voltage divider resistors 62 and 63 while the suppressor grid id is connected to its cathode :12 in a conventional manner. The control grid 13 is connected through a grid resistor '19 to a third terminal 86 of the current regulator assembly 36 for connection to the voltage of the generator i in a manner to be described presently. A bypass capacitor 5! is connected across the saturating coil 36.

A portion of the voltage of generator l to be regulated is applied between the regulator terminals 5B and 86 and in the form illustrated these terminals are connected to output terminals 62 and 83, respectively, of the section of the regulator ident fied as the current standard.

A third output terminal 6 of'the current standard is connected to terminal 62 of the current regulator and forms the negative bus of the regulated anode supply for the current standard. The term nal 40 is maintained at a positive potential with respect to terminal til and is connected through terminal 82 and a switch 85 to the positive side of output circuit 2 of generator 5 and also supplies a positive potential to the anode of the control tubes of the current standard.

The current standard above referred to comprises an electronic control network preferably encased in a constant temperature box or compartment indicated by the dotted rectangle 66.-

The current standard may be divided into four circuits which may be identified as a reference fiuxmeter 81, a monitor fiuxmeter 88, a feedback circuit 89 and a compartment heater circuit 90. The particular arrangement of the elements and control circuits of the current standard per se are the invention of Theodore A. Rich and are described and claimed in his'copending application Serial No, 655.982 filed concurrently herewith and assigned to the assignee of the present application. The reference fiuxmeter Bloomprises, broadly speaking, a compensated galvanometer of the type described and claimed in Patent No. 2,356,608, granted August 22, 1944 upon an application of Lorin OBryan. The term "compensated as used in connection with this galvanometer means that the meter does not tend to drift either to a zero or to a stop position at either end of its travel. Since the specific details of the fluxmeter per se form no part of my,

invention, I have illustrated the essential elemerits of the device in a simplified diagrammatic form as comprising a magnetic core 9| within which is suspended a coil winding 92 by means of wires 93 and 94, which are preferably of gold. A mirror 80 is mounted on the wire 94. The fluxmeter is similar to a direct current milliammeter except that it has no restraining torque and very little friction in view of the gold wire suspension. Whatever restraining torque is introduced by the gold wire suspension is canceled out by a tiny permanent magnet 90 operating in the stray field of the magnet 9|. Adjustment of the stray field is obtained by soft iron magnetic field shunting elements 91 and 98 which are adjustable towards or away from-the magnet 98. The closer these two soft iron pieces are to the small torque-compensating magnet 96, the less the restraining torque is canceled out, and vice versa. Manual control of the fluxmeter position is obtained by means of a reversing switch 99 which connects the coil 92 for energization of either polarity from a, battery I through a resistor MI. The switch 99 is biased to a neutral contact position by suitable means indicated as springs 99. The primary standard in the current standard is a standard cell I02, the voltage of which is compared with the voltage drop across a resistor I03. The resistor I03 and a control tube I 04 are connected across bus conductors I05 and I08 which are energized from the regulated voltage supply input terminals 82 and 84 from the current regulator 39. In order to protect the standard cell. arelay I01 is provided and comprises an operating coil I08 connected in series with resistor I03 and control contacts I09. 1

The contacts I09 connect the standard cell I02 in differential relation with the voltage drop of resistor I03 across the coil 92. A voltage divider comprising resistors H0 and III is connected in series across the regulated voltage supply conductors I05 and I06. Resistors H0 and III are provided with adjustable taps H2 and H3, respectively. The tube I04 is provided with an anode II4, a cathode H5 and a control electrode or grid H8. An anode resistor H1 is connected in series with anode H4, and the cathode H5 is connected to the adjustable tap II3 on resistor III. A voltage divider comprising in series relation a resistor I I8, a light sensitive device such as a phototube H9, and a resistor I20 is connected between the adjustable tap II2 of resistor H0 and to the conductor I06. The grid H6 or tube I04 is connected to a junction terminal II6 between the phototube I I9 and the resistor I20. The

resistance of the phototube is controlled in accordance with the amount of light striking its target as directed thereon by the mirror 95 of the fluxmeter fromv a source of light I2I and thereby controls the potential of grid l6.

It may be helpful at this point to consider the operation of the reference fiuxmeter 81. By placing the reversing. switch 99 in one position or the other, a voltage is impressed on the fluxmeter coil 92 from battery I00 to force coil 92 to rotate in one direction or the other to a given position. The phototube H9 and resistors H8 and I20 form a voltage divider circuit to control the grid II6 of tube I04. As soon as tube I04 is rendered conductive by the initial positioning of coil 82, the relay I08 picks up to close its contacts I09 and thereby connect coil 92 of the fluxmeter for energization in accordance with the differential voltage of the standard cell I02 and the drop across resistor I03. Since the fluxmeter will rotate in one direction as long as voltage tively, to the terminals of resistor I25.

the light beam further on the phototube I I9 to in-- crease in a positive direction the potential of grid I I8 and thereby increase the current through resistor I03 and establish a state of voltage equilibrium with the voltage of the standard cell. If for any reason, such as failure of the light source I2I, the anode current to tube I04 drops below the predetermined value required to give the desired drop across resistor I03, the relay I01 will drop out and open the circuit of standard cell I02. After reestablishing the light source, the light beam will have to be projected on the phototube II9 by means of the manual control switch 99 which may be momentarily operated to an energizing position to actuate the relay coil I08 and establish the desired grid potential on grid H8.

It will have been observed from the foregoing description of the reference fluxmeter 81 that a standard voltage equal to the voltage of the standard cell I02 will be obtained across resistor I03. The standard voltage obtained across resistor I03 will be as standard as that of the standard cell, making it possible to tap of! different voltage components having the characteristics of the voltage of the standard cell without drawing any current from the standard cell. This standard voltage drop across resistor I03 is.divided into steps by the arrangement of resistors I22, I23, I24 and I25. Resistors I22 and I24, which may be fixed resistors, are connected in series relation with the resistor I23 of the variable type across the voltage standard resistor I'03. The resistor I23 is provided with two adjustable arms I26 and I21 adjusted in spaced relation on the resistor I23 and connected, respec- If de sired, the arms I26 and I21 may be tied together mechanically to preserve a given spaced relation the same as the reference fiuxmeter 31 except that it may be provided with a lower resistance coil I29 cooperating with its magnetic core I30. The coil I29 is suspended by gold wires HI and I32 and a mirror I33 is mounted on the wire I32. The adjustment for the stray field is obtained by the small magnet I34 and the soft iron pieces I35 and I38 placed in the stray field of the magnet I30. Manual control of the fluxmeter 88 is obtained by means of a reversing switch I31 biased to a neutral contact position by suitable means indicated as springs I31. The switch I31 controls the monitor fluxmeter coil I29 through a resistor I29 from battery I00 in the same manner as switch 99 controls the reference fiuxmeter coil 92; in other words, it initially positions the coil I29 to a desired operating position. A voltage divider, comprising resistors I38 and I39 connected in series relation across conductors I05 and I00 of the regulated voltage supply, is provided for thecontrolled circuit of the monitor fluxmeter 88. The resistors I38 and I39 are provided, respectively, with adjustable arms I40 and I. A voltage divider comprising a resistor I42,

a phototube I43 and a resistor I44 is connected in series relation between the adjustable arm I40 of resistor I38 and the bus conductor I06. The resistance of the phototube I43 is controlled in accordance with the amount of light striking its target as directed thereon by the mirror I33 by a source of light I45. A control circuit for the monitor fluxmeter comprises a resistor I46 connected in series relation with transformer I41 constituting a mutual inductance and a controlled electronic tube I48 between the regulated bus conductor I and the adjustable arm I4I on voltage divider resistor I39. The tube I48 is provided with an anode I49, a cathode I50 and a control electrode or grid I5I. The grid I5I is connected to a junction terminal I5I between phototube I43 and resistor I44. A capacitor I52 is connected between the grid I5I and its cathode I50 for preventing the grid from changing its potential too quickly. The transformer I41. or mutual inductance. comprises a primary winding I53 connected in series with the anode-cathode circuit of tube I48 and a secondary winding I54.

The secondary winding I54 is connected in series relation with the coil I29 of the monitor fiuxmeter and through a resistor I55 to the negative terminal of a current shunt I56 which, in turn, is connected in the positive output conductor 2 of generator I. The positive terminal of shunt I56 is connected to the positive bus conductor I05 and also to the controlled circuit including the primary winding I53 of the mutual inductance and the controlled tube I48. The monitor fluxmeter thus compares the component of voltage across shunt I56 with the voltage component derived from the secondary standard constituted by the voltage divider resistor I25 and the associatedresistors I22, I23 and I24. The comparison circuit may be traced from the positive terminal of shunt I56, conductor I05, resistors I24,

I23 and I25 and adjustable arm I28, through coil I29, thence through secondary winding I54 and resistor I to the negative terminal of shunt I 56. The mutual inductance I41 having its primary winding I53 in series relation with tube I48 slows down any change in energization of the circuit of coil I29 by inducing a voltage therein which tends to rotate the element I29 in such a direction as to oppose the change of current in the circuit of tube I48. having one set of contacts I58 and another set of contacts I59 is provided to connect a voltage reg- A double-poled switch I51 ulating glow tube I60 through contacts I50 to the Y anode of tube I 48 and to theregulated bus conductor I06 and also toconnect the glow tube I60 through contact I59 to the terminal 80 of the current regulator through terminal 83.

The feed-back circuit 89 is utilized to insert a cuit in accordance with voltage changes of generator I and comprises a voltage divider I6I convoltage component in the monitor fiuxmeter cirnected to be responsive to the voltage of generator I and includes in series relation adjustable resistors I62, I63, I64-and I65 connected across the positive and negative terminals of generator I through a fixed resistor I66. The resistor I63 is provided with an adjustable arm I61 which is connected through series connected resistors I68 and I69 to the contacts I59 of switch I51. The

resistor I65 is also provided with an adjustable arm I65 whichmay be connected mechanically, as indicated by the dotted line. to operate in unison with arm I26 of resistor I23. A junction terminal I10 is provided between the resistors I68 and I69 which is connected to output terminal 7 terminal 40.

the voltage divider I6I and with resistor I66 forms a filter to reduce the voltage ripple on the voltage divider I6I Energy storage means such as a capacitor I12 is charged through resistor I66 from the negative generator terminal in a circuit including resistor I13. resistor I55 in the circuit of fluxmeter coil I29 to the negative side of shunt I56 in the positive conductor of generator I. The capacitor I12 and its associated circuit elements constitutes an anti-hunting circuit and is arranged to charge or discharge when the voltage of generator I changes through the resistor I55 and thereby insert a component of voltage in the circuit of coil I29 of the monitor fluxmeter. Since capacitor I12 may hold its charge upon removal of the current standard panel for inspection or repair. it is desirable to short circuit this capacitor as indicated by the grounding switch I14.

The heater circuit 90 is provided to maintain the temperature of the current standard compartment 86 at a constant temperature and, as illustrated, this heater circuit comprises a heater element I15 preferably positioned near the bottom of the compartment with thermostat I16 and suitable fuse elements I11 all connected in series relation to be energized from the alternating current supply circuit I2.

The operation of the current regulator is substantially as follows: The current regulator itself controls generator voltage when switch I51 is open and switch is closed (both in the current standard). Constant voltage is maintained between the current regulator terminals 40 and 42 by the action of series regulating tube 41 which in efiect is a variable impedance between the output terminals 40 and 42 and the supply voltage of transformer 25. Grid control for tube 41 is obtained in accordance with the voltage drop across resistor 58 and this voltage, in turn, is dependent upon the grid-to-cathode voltage of amplifier tube '52, as determined by the differential voltage between'the component of voltage across resistor 61 and the fixed component of votage established by glow tube 60. Let it be assumed that the voltage of the power supply conductors 44 and 66 tends to increase. This causes an increased voltage drop across resistor 61, increases the positive potential of grid 55 of tube 52 and thereby increases its anode current} The increase in anode current of tube 52 increases the current in resistor 56 and thereby makes the grid of the series regulating tube more negative so as to bring the reference voltage across conductors 44 and 86 back to normal. A standard voltage of reference is thus provided between the terminals 40 and 42. The voltage divider I6! is connected across the terminals of generator I and a voltage proportional to the voltage of generator I is introduced into the current regulator between terminals 40 and 4| and compared with the reference voltage. The portion of the voltage obtained from generator I is applied to the terminals 40 and BI in such a way as to make terminal (II negative with respect to Terminal 4| is connected to the grid of amplifier tube 10. Now assume that the voltage of generator I rises. As a result, the voltage between terminals 40 and 4| increases and causes the grid 13 of tube 10 to become more negative, thereby decreasing the anode current of tube 10. This anode current is the direct current saturating current of saturable reactor 2! and the decreased saturation increases the reactance and thereby increases the angle of lag of the grid voltage of rectifier 8. This results in a reduced current output from the tubes I and II which, in turn, reduces the generator excitation so that thegenerator voltage drops back to normal.

, The foregoing description of the generator has been with reference to the regulator as a voltage control device. When used with the current standard with switch I51 closed, the regulating system becomes a current regulating device. This is accomplished by the action of the current standard in comparing a component of voltage from the current shunt I56 and a component of voltage derived from the standard voltage obtained from resistor I25 and its associated voltage divider resistors. The difference voltage thus obtained is amplified to modify the generator voltage introduced between the current regulator terminals 46 and ll. When switch I51 is closed, terminal 83 of the standard which is connected through terminal 4| to the grid of amplifier tube 10 assumes the average voltage of the tap I61 on resistor I63 and the anode voltage of tube I48. This average voltage varies in accordance with the operation of the monitor fluxmeter 88. When the voltage component across the shunt I55 is greater than the standard reference voltage, the fiuxmeter coil I29 rotates to throw more light on the phototube I43. More light on the phototube I43 increases the positive potential of grid I5I of tube I48 and causes this tube to conduct more current. The increase of current in the circuit of tube I48 tends to lower the average potential of terminal 83 and thereby the grid potential of amplifier tube Ill of the current regulaton. As a result, through the action of the phase shifter 24 the excitation of the generator I is decreased in the manner heretofore explained and the current output of the generator is returned to the desired value as determined by an equilibrium condition between the voltage component of shunt I56 and the standard reference of the current standard section of the regulator.

While I have shown and described my invention as applied to a particular system of connections and as embodyin various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may.

be made without departin from my invention, and I. therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I ciairn as new and desire to secure by Letters Patent of the United States is:

1. In combination, an electric circuit to be controlled, means for controlling said circuit, means for providing an electric quantity having a constant value, means for comparing an electric quantity of said circuit with said electric quantity of constant value and for providing a, controlling electric quantity variable in accordance with the ,diiference between the electric quantity of constant value and the electric quantity of said electric circuit, control means responsive to said controlling electric quantity for controlling said first mentioned means, means for deriving a second electric quantity from said electric circuit, a standard of reference, means for comparing said second electric quantity with said standard of reference for providing a differential quantity variable in accordance with the departure of said second electric quantity from said standard of reference, and means responsive to said diflferen- 10 tial quantity for modifying the operation of said control means.

'2. In combination, an electric circuit to be controlled, means for controlling said circuit, means for providing a component of voltage having a constant value, means for deriving a component of voltage from said electric circuit, means for comparing said components of voltage for'providing a differential controlling component of voltage, control means responsive to said differential component of voltage for controlling said first mentioned means, means for deriving a second component of voltagecorresponding to the current in said electric circuit, a standard of reference for providing a constant component of voltage, means for comparing said second component of voltage and the component of voltage from said standard of reference for providing a second differential controlling component of voltage variable in accordance with the current of said circuit, and means responsive :to said second differential component of voltage for modifying the operation of said control means.

3. In combination, an electric circuit to be controlled, electronic regulating means responsive to the voltage of said electric circuit for controlling the voltage of said electric circuit, means independent of the current of said electric circuit for providing a current standard of reference, means for comparing the current value of said circuit with said current standard of reference to provide a differential electric quantity, and means for modifying the operation of said electronic regulating means in accordance with said differential electric quantity to maintain the current in said electric circuit at a value proportional to said current standard of reference.

4. In combination, an electric circuit to be controlled, electronic regulating-means connected to be responsive to the voltage of said electric circuit for controlling the voltage thereof, means for providing a Current standard of reference, means for comparing the value of current oi. said circuit with said current standard of reference to provide a differential electric quantity, and switching means for selectively connecting said voltage responsive means for energization in accordance with said differential quantity to change said regulating means-from a voltage regulator to a current regulator.

5. In combination, an electric generator for energizing a variable resistance load, an excitation circuit for said generator, a voltage regulator connected to be responsive to the voltage of said generator for controlling said excitation circuit,

means independent of the current of said generator for establishing a current standard of reference, means for comparing the current of said generator and said current standard of reference,

and means for maintaining the current of said generator constant irrespective of variations in its load resistance comprising means for modifying the operation of said voltage regulator in accordance with the departure of the current of said generator from said current standard of reference.

6. In combination, a direct current generator having an output circuit for energizing a variable resistance load, an excitation circuit for said generator, means comprising a rectifier including a pair of electronic tubes for controlling the energization of said excitation circuit, means for controlling the output of said rectifier including a direct current winding, a source of regulated voltage, means including a control electronic tube 11 having a control electrode and connected to be energized from said source of regulated voltage for controlling the energization of said direct current winding, means for obtaining a component of voltage variable in accordance with the difference between the voltage of said source and the voltage of said generator for controlling said control electronic tube, a current standard of reference, a current shunt in said output circuit, means for connecting said current standard of reference and said current shunt in differential relation for producing a differential comp-onentof voltage, and means for modifying the potential of the control grid of said control electronic tube in accordance with said differential component of l voltage.

I age, means including a control electronic tube connected to be energized from said source of re ulated voltage for controlling the energization of said direct current winding, said control electronic tube having an anode, a cathode and a control electrode, a voltage divider including a. plurality of resistors connected in series relation across the output circuit of said generator and having an intermediate junction terminal connected to said control'electrode, a current standard of reference,

a current shunt in said generator output circuit,

means for obtaining a differential component of voltage variable in accordance with the departure of the current of said shunt from said current standard, switching means for connecting said differential voltage to said voltage. divider for modifying the voltage applied to said control electrode from said junction terminal, a glow discharge device for providing thereacross a con stant component of voltage when energized, and switching means simultaneously operative with said first mentioned switching means for connecting said glow discharge device in the anode-oath:

ode circuit of said control electronic device.

8. In combination, a source of constant voltage, a second source of voltage subject to variation connected in series differential relation with said source of constant voltage, means for controlling said secondsource of variable voltage including an electric winding connected to be energized in accordance with the differential component of voltage between said sources of voltage, energy storage means connected to said second source and responsive to a change in voltage of said second source for introducing a component of voltage in the circuit of said electric winding, and means responsive to the differential component of voltage between said sources of voltage for maintaining .a state of equilibrium therebetween.

9. In combination, a source of constant voltage, a second source of voltage subject to variation connected in series differential relation with said source of constant voltage, means including an electric winding connected to be energized in accordance with the differential component of voltage between said sources of voltage, means for controlling said second source of voltage, means.

comprising a capacitor connected to be charged from said second source and connected'in ciruit with said electric 'winding for introducing therein a component upon any change in voltage of said second source, and means responsive to the ener- .gization of said electric winding for controlling said second mentioned means to maintain equilibrium between said second source of voltage and said source of-constant voltage.

10. In combination, an electric generator for energizing a variable resistance load, an excitation circuit for said generator, a voltage regulator connected to be responsive to the voltage of said generator for controlling said excitation circuit, a current standard of reference including an electric winding, means for maintaining the current of said generator constant irrespective of variations in itsload resistance comprising means for modifying the operation of said voltage regulator in accordance with the departure of the current of said generator from said current standardof reference, and anti-hunting means comprising modifying the operation of said voltage regulator in accordance with the departure of the current of said generator from said current standard of reference, and anti-hunting means comprising a capacitor connected'to be responsive to a change in the voltage of said generator for introducing a component of voltage in the circuit of said electric winding.

JERRY L. STRATTON.

REFERENCES CITED The followingreferences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,057,490 Jenks Oct, 13, 1936 2,074,947

Stratton Mar. 23, 1947 Certificate of Correction Patent No. 2,452,611. November 2, 1948.

JERRY L. STRATTON It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 2, line 42, for is is provided read is provided; column 3, line 60, for the Word position read positive; column 12, line 13, claim 9, after component insert of voltage;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 24th day of May, A. D. 1949.

THOMAS F. MURPHY,

Assistant Uommissioner of Patents.

Certificate of Correction Patent No. 2,452,611. November 2, 1948.

JERRY L. STRATTON I It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 2, line 42, for is is provided read is provided; column 3, line 60, for the word position read positive; column 12, line 13, claim 9, after component insert of voltage;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 24th day of May, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

